The present invention is related to heat sinks for printed circuit boards, and more particularly to a system and method of transferring heat from electronic devices using a surface mounted conduction heat sink.
Circuit boards are becoming more and more densely packed with electronic devices as the need for power, memory and additional capabilities increases. As a result the heat generated by these electronic devices also increases. The heat that is generated by an electronic device must be transferred away from the electronic device or the performance of the electronic device(s) will deteriorate. The problem of dissipating heat from electronic devices mounted on circuit boards gets worse when the piece of equipment employing the circuit board is mounted within a housing. For example, fiber optic transmitter/receiver modules that include circuit boards are often environmentally sealed in a housing to prevent damage from the elements. As a result, the ability to dissipate heat from the electronic devices mounted on the circuit boards becomes challenging. The environmental housing""s only mode of heat transfer to the ambient is natural convection. The transmitter/receiver module""s only mode of heat transfer to the environmental housing is conduction.
A classic thermal management technique uses thermal vias to dissipate heat. The thermal vias are located in a copper pad of a printed circuit board, under the device that needs cooling. A heat sink pad of a device is soldered to the copper pad of the circuit board. During operation of the device, heat is transferred from the device""s heat sink pad to the copper pad on the primary side of the circuit board. The heat is then transferred through the thermal vias to the far (secondary) side of the circuit board and to the housing of the transmitter/receiver module. The heat is then transferred by conduction from the transmitter/receiver module to the unit""s environmental housing. As the component density in an electronic module increases, it becomes difficult to use classical thermal vias to dissipate heat.
The above mentioned problems with meeting the thermal requirements of electronic devices mounted on circuit boards are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a printed circuit board is provided. The printed circuit board includes a first heat transfer pad on a surface of the printed circuit board and an electronic device having a top surface and a bottom surface, the bottom surface includes a second heat transfer pad. The second heat transfer pad is coupled to the first heat transfer pad. The printed circuit board includes a heat sink mounting pad on the surface of the printed circuit board, the heat sink mounting pad is located adjacent to and thermally coupled to the first heat transfer pad. The printed circuit board further includes a heat sink coupled to the heat sink mounting pad, the heat sink is thermally coupled to the electronic device.
In another embodiment, an environmentally sealed housing for a fiber optic transmitter/receiver module is provided. The housing includes a printed circuit board having a primary and a secondary surface. The primary surface includes a first heat transfer pad and a heat sink mounting pad adjacent to and thermally coupled to the first heat transfer pad. The housing includes an electronic device having a top and a bottom surface. The bottom surface includes a second heat transfer pad that is coupled to the first heat transfer pad. The housing further includes a heat sink coupled to the heat sink mounting pad. The heat sink is thermally coupled to both the electronic device and the environmentally sealed housing.
In a further embodiment, a heat sink is provided. The heat sink includes a pair of substantially parallel vertical legs and a horizontal member coupled between the legs to form a xe2x80x9cUxe2x80x9d shape. The horizontal member includes an outer surface and an inner surface both having a layer of thermal interface material. The heat sink is surface mountable to a heat sink mounting pad on a surface of a printed circuit board. The heat sink mounting pad is adjacent and coupled to a heat transfer pad of an electronic device. The heat sink adapted to be thermally coupled to the electronic device.